A conventional lock includes a housing, a central cylinder and a plurality of tumbler units. The central cylinder is inserted into the housing, is rotatable relative to the housing, and has a straight keyway that is formed through an insertion end thereof. Each of the tumbler units includes first and second pins that are mounted movably between the housing and the central cylinder. The first pin extends into the keyway. The second pin abuts against one end of the first pin distal from the keyway. Each of the tumbler units is operable to switch between a locking state, where the second pin of the tumbler unit is inserted into both of the housing and the central cylinder to prevent the relative rotation between the housing and the central cylinder, and an unlocking state, where the first and second pins are retracted respectively into the central cylinder and the housing to permit the relative rotation between the housing and the central cylinder.
The first pin of each of the tumbler units can be accessed by a straight key blade that is inserted into the keyway, such that each of the tumbler units can be driven to switch to the unlocking state to permit the relative rotation between the housing and the central cylinder. However, the conventional lock is easily picked since a picking tool may be easily inserted into the straight keyway to access the first pins of the tumbler units.